Cathode ray oscillograph



Oct, 24, 1933. A. M. OPSAHL CATHODE RAY OSCILLOGRAPH Filed Aug. 14, 1929 Li? a I w ATTOR N EY Patented Oct. 24, 1933 CATHODE RAY OSCILLOGRAIPH Alert M. Opsahl, Wilkinsburg, Pa.,- assigncr to Westinghouse Electric 8; Manufacturing Com= pany, a corporation of Pennsylvania Application August 14, 1929. Serial No. 385,840

2 Claims.

My invention relates to cathode-ray oscillographs and particularly to cathode-ray oscillographs which comprise a combination of shields and deflecting plates for preventing the cathode ray or electron beam from reaching a photographic plate or film until the beam is so defiected as to pass by the shields.

When an oscillograph of the above-mentioned type is employed for automatically recording any disturbances which may occur on a transmission line, difliculty is often encountered because of the photographic plate or film becoming fogged, before the disturbance occurs, by stray electrons from the beam. Because of this tendency of the plate to fog during the period that the apparatus is maintained in operative condition for recording a transient, it has been impossible to make that period longer than two hours and still have the photographic surface in condition to make a clear record.

It has been found that the fogging is caused by the slower-moving electrons in the cathode beam. These electrons reach the photographic plate and fog it because they are more easily deflected than the higher-speed electrons and are deflected past the shields by the normal line voltage.

An object of my invention is to so design an oscillograph of the above mentioned type that it may be connected'to a transmission line for a long period, while in operative condition, without the photographic surface becoming fogged.

More specifically, an object of my invention is to reduce the tendency of the photographic surface to become tagged, in apparatus of the above mentioned type, by removing the more slowlymoving electrons-from the electron beam.

A further object of my invention is to provide an electron beam from which the slower-moving electrons have been removed whereby the beam may be focused to a sharper point on the fluorescent screen or photographic plate.

In practicing my invention, I provide an evacuated elongated casing which consists of two sections and which'ha's means, at one end thereof, for generating an electron beam and for projecting said beam longitudinally of the casing. A sensitized recording surface may be provided at the other end of the casing for intercepting the electron beam. w

Shields and deflecting plates are positioned in the lower section of the casing for preventing the electron beam from being impressed upon the fluorescent screen or photographic surface until the phenomenon to be recorded occurs, and for plates and a baffle are positioned to separate the then deflecting the beam in accordance with the character of the phenomenon. This portion of the apparatus is described and claimed in copending applications, Serial Nos. 238,505 and 296,844, filed on December 8, 192'? and August 543 l, 1928, respectively, in the name of Ernst H. Norinder, and assigned to the Westinghouse Electric and Manufacturing Company.

In the upper section of the casing, deflecting more slowly moving electrons in the electron 66 beam from the remaining electrons.

Other features and advantages of my invention will appear from the following description, taken in connection with the accompanying drawing, in which Figure 1 is a view, in longitudinal section, taken on the line II of Fig. 2, of an oscillagraph constructed in accordance with my invention;

Fig. 2 is a view, in longitudinal section, taken on the line II-II of Fig. 1; and

Fig. 3 is a diagram of the electrical connections of an oscillograph constructed in accordance with my invention.

Referring to Figs. 1 and 2, the apparatus comprises a metal envelope or tube 1, the lower end of which is enlarged to provide a chamber 2 for a photographic plate or film 3. The lower-end of the chamber 2 is closed by means of a plate 4 which is secured, by means of bolts 5, to a flange 6 extending from the tube 1. The joint between the plate 4 and the flange 6 is maintained gas-tight by means of a rubber gasket 7.

The upper section of the evacuated casing comprises a metallic envelope or tube 8 which is secured to the lower section 1 by means of a conical joint.

The upper end of the tube 8 is closed by means of a plug 9 having a tube 10 of insulating material, such as glass, secured thereto and projecting axially from the tube 8. The upper end of the tube 10 is provided with a cap 11 centrally apertured to permit the passage therethrough of the terminal of a cathode 12. The cathode terminal is enlarged as at 13, to completely close the aperture in the cap 11.

A suitable sealing compound may be employed to secure the several elements together. Preferably, a cold cathode is employed but, obviously, a hot cathode may be employed, if desired.

An anode 14 is secured to the lower end of the glass tube 10 and is provided with an axial aperture so thata portion of the electrons projected from the cathode 12 to the anode 14 will pass therethrough. The anode i4 is provided, it neceasary, with suitable water cooling means.

As the electron beam passes through the upper section 3 of the casing, the more slowly moving electrons are removed from the beam, as will be more fully explained hereinafter. Therefore, when the electron beam enters the lower section 1 or the casing, it comprises electrons having a comparatively uniform velocity A frame which consists of two balrelite strips 15 supported at their respective ends by means of bakelite rings 16, is supported inside the metal tube 1. Metal deflecting plates 17 are supported at the upper end of the frame, each plate being secured to one of the bakelite strips 15. Deflecting plates 18 constituting a second pair are likewise supported by means of the bakelite strips 15 near the middle of the frame. The deflecting plates 17 and 18 are electrically connected to the terminals 19 and 20, respectively, which extend through hollow metal conical plugs 21 and are supported therein and insulated therefrom by means of a suitable insulating material.

' A target 22, comprising a strip of metal, is positioned between the two pairs of deflecting plates 17 and 18 and on the longitudinal axis of the oscillograph. The metal strip 22 is eccentrically mounted on the conical metal plug 23 which is fitted into the wall of the casing l. The width of the target 22 is approximately equal to the diameter of the aperture in the shield 24.

The shield 24 consists of either a bakelite or metal plate which has an aperture in the middle thereof. It is secured to the bakelite strips 15 below the second set of deflecting plates.

A concentration coil 25 of the type well known in the art, is preferably positioned outside the casing 1 and surrounds the shield 24.

Deflecting or timing plates 26 are positioned below the shield 24 in a plane at right angles to the deflecting plates 17 and 18 and are supported by means of brackets 27 secured to the bakelite strips 15. The timing plates 26 are electrically connected to terminals 28 which extend through, and are insulated from, conical bushings 29.

Another frame, comprising two bakelite strips 30 supported at their respective ends by means of bakelite rings or discs 31, is supported inside the upper metal tube 8. Three pairs of metal deflecting plates are supported on the bakelite strips 30, the pairs of deflecting plates being positioned one below the other. The upper deflecting plates 32 are electrically connected to terminals 33 which extend through, and are insulated from, conical metal bushings or plugs 34. The middle deflecting plates 35 and the lower deflecting plates 36 are similarly connected to terminals 37 and 38, respectively, which extend through the conical bushings 34.

A bafile or screen 39, preferably comprising a rectangular metal plate is positioned between the two upper pairs of deflecting plates 32 and 35 and is secured to a bakelite strip 30 by means of a bracket 40. The baiiie '39 is located in a horizontal position at right angles to the deflecting plates and extends to a point intermediate the deflecting plate nearest to it and the longitudinal axis of the tube in order to intercept the more widely deflected electrons. The upper and lower supporting rings or discs 31 of the frame have small apertures in the middle thereof to permit the main electron beam to pass therethrough and, at the same time, to obstruct the passage of stray or scattered electrons.

neeacea The electrical connections of-the apparatus are shown in Fig. 3. The negative terminal of a high-potential direct-current source 41 is connected to the cathode 12, and the positive terminal of thesame source is connected to ground. The anode 141s also grounded so that a high potential is maintained between the cathode and the anode to generate the electron beam. The right-hand plate of the. upper pair of plates 32, the left-hand plate of the middle pair of plates 35 and the right-hand plate of the lower pair of plates 36 are connected to the positive terminal of the high-potential battery 42, which terminal is connected to ground.

The left-hand plate of the upper pair of plates 32, the right-hand plate of the'middle pairvof plates 35 and the left-hand plate of the lower pair of plates 36 are connected to the negative terminal ofthe battery 42. The bame plate 39 is preferably grounded.

In the lower section, the right-hand plate of the upper pair of plates 1'7 and the left-hand plate of the lower pair of plates 18 are connected to ground. The left-hand plate of the upper pair of plates 17 and the right-hand plate of the lower pair of plates 18 are connected to a point on an electrostatic potentiometer 43 which is connected between a transmission line 44 and ground. The potentiometer comprises a plurality of condensers connected in series. target 22 is preferably grounded.

One-of the timing plates 26 is connected to ground while the other timing plate is connected to one terminal of an alternating-current source 45, the other terminal of the alternatingcurrent source being connected to ground.

The operation of the apparatus with the deflecting plates 32, 35 and 36 in the upper section inactive, will first be described. Under these conditions, as soon as a high potential is impressed on the cathode 12, an electron beam is generated which is projected through the aperture in the anode 14 along the longitudinal axis of the tube. When there is normal potential on the transmission line 44, the electron beam enters the lower section of the casing and strikes the target 22, since the voltage impressed on the upper plates 17 is not sufficient to deflect the electron beam to one side of the target. Therefore, the main electron beam is prevented from reaching the photographic plate 3. However, when a surge appears on the transmission line 44, the electron beam is deflected past the target 22, so that it passes between the lower deflecting plates 18. The deflecting plates 18 again deflect the beam, but in the opposite direction to the first deflection, and the electron beam passes through the aperture in the shield 24 and strikes the photographic surface 3.

The deflecting plates 17 and 18 and the shield 24 are so adjusted with-respect to each other that the electron beam passes through the aperture in the shield 24, irrespective of the angle at which the beam is deflected. The alternating current, which is continuously impressed on the timing plates 26, causes the electron beam to be deflected at right angles to the first deflection to give it a time component.

In operating the apparatus in accordance with my invention, a potential is impressed on the deflecting plates 32, 35 and 36 in the upper section, as indicated in Fig. 3. Then, when the electron beam passes between the upper deflecting plates 32, it is deflected toward the right-hand plate,

. the more slowly-moving electrons being deflected The,

to a greater extent than the other electrons, as indicated vby the dotted line 46 in Fig. 1. With the apparatus properly adjusted, the slowly-moving electrons are intercepted by the baflle plate 39, while the remaining electrons, which constitute the main electron beam indicated by the dotted line 4'7, pass by the edge of the baflie plate and enter the field of the middle deflecting plates 35. The middle deflecting plates deflect the electron beam in a direction opposite to the first deflection. The electrons then enter the electrostatic field or' the lower deflecting plates 36 and are so deflected as to direct the electron beam along the longitudinal axis of the tube.

When the electron beam enters the lower section, it is there acted upon by the deflecting plates 17 and 18, as previously described. In this case, however, the more sensitive electrons have been removed and there are no electrons in the electron beam sensitive enoughto be deflected around the target 22 by the normal line voltage.

Various modifications may be made in my invention without departing from the spirit and scope'thereof, and I desire, therefore, that only such limitations shall be placed thereon as are shown by the prior art and set forth in the appended claims.

I claim as my invention: v

1. Electrical apparatus comprising a casing, means in said casing for generating a beam or charged particles, an obstruction in the normal path of travel of said particles within said casing, means for bending said beam of charged particles to one side of said obstruction and means including a deflecting device for removing the slower moving particles from said beam before they reach said obstruction.

2. Electrical apparatus comprising a casing, means in said casing for generating a beam of charged particles, an obstruction in the normal path of travel or said particles within said cas--- ing, means for bending said beam of charged 90 particles around said obstruction, means for deflecting said be by a constant field in one direction before the particles reach said obstruction whereby the slower moving particles of said beam are deflected by greater amounts than the remaining particles, and means for obstructing only the paths taken by said slower moving particles when deflected by said constant field. v

ALERT M. OPSAHL. 

